Swapped carbs & opened the muffler on my MS260. Wow!

[rustyb]

Well, I finally did it and can not believe the difference it made! The saw screams now compared to how it ran stock. In fact, I had to check several times that it wasn't too lean on the HS screw being that I wasn't used to it reving so freely & quickly. And, I didn't even open the muffler all the way as Timberwolf tested (my opening is 15/32" x 3/4" as opposed to 7/16" x 1 1/2"). It amazes me how much performance was locked up! (I may open it up a tad more later...don't know)

Anyhow, not that I'm an expert by any stretch, but I'm comfortable saying if you have a newer MS260, you should consider doing these mods. They are easy, cheap (if you find a used carb) and will make this saw run the way I'm sure it was intended not to mention last longer. For what it's worth, I used an older Walbro 026 carb and put the metering diaphram cover from my non-adj carb on it. So, unless I'm mistaken, it's now a fully adj Intelli Carb.

Thanks to everyone here who has posted info about this and answered all my silly questions. Thanks also to Sedanman for giving me a heads up on a carb (even though I didn't get that one) and Jacob J for the carb and all his valuble insight.

rusty

 

[123Michael]

before i comment take note... i am NOT an engineer, nor do i have extensive experience in modifying chainsaws ( i have rebuilt a few small ones) so take what i say with a grain of salt

I have had a lot of experience with engines generally (ie car engines). when you modify to get more power you also have to modify for extra strength. ie forged pistons, shot rods, balanced and blue printed, better rings, hardened valves and all that.

I guess the same would apply to a chainsaw. you may be getting an extra 20% more power but there is a good chance the saw will fail a lot sooner.

I was reading my stihl manual and it said that my saw is not designed to rev above 10,000 rpm. it was said in the context of leaning out the high jet, however, it did NOT say the damage would be caused by too lean a mixture, just from revving too hard.

I guess if the saw lasts another 10 years with fair use then the engine has been satisfactorily over engined at the factory. however i suspect that the probability that the saw will fail sooner will be increased.

 

[sedanman]

123Michael, Welcome. The generally held opinion is that the restritions put on the saw by the EPA (environmental protection agency) are more harmful to saw life than "opening them up". The saws are reported to run cooler and that has to be a good thing. Also, a fully adjustable carb in the hands of someone who knows how to tune it assure the correct mixture, not something that the EPA thinks is "acceptable".

 

[Kneejerk Bombas]

Michael brings up an interesting point. Do you all think that the saw makers will start to make the engine components lighter duty, now that they make less power?

 

[bill147]

If EPA regs cause the saws to run hotter, it would make sense that the saw designers would tweak their design tolerances to match a hotter running saw.

I'm sure that the stihl, husky, etc designers are not going to allow EPA to shorten the useful lifespan of the saw.

EPA emission regs are out of their control, but saw life certainly is.

Just my two cents worth!

 

[dozerdan]

123Michael
I am not sure if they have attacked your saws with emission controls but they sure did with saws shipped into our states.
The 260 is a prime example of an EPA saw.It is the same basic saw as the older 026 with the exception of the non adjustable carb and added the feature of a compression release.Same crank,piston,cylinder is the same other than the added hole for the decompression valve.According to my Stihl charts,the 026 has a Max RPM of 12,000-13,000.That's the maximum speed that all of the internal parts are designed to run at,no load.Our new 260 has a fixed main jet in the carb that causes the saw to run way lean.Remember we have to make EPA happy.Lean mixtures does burn up pistons.To make matters worse that little 260 hold in more heat yet from the super restricted muffler.They make all of the exhaust from that engine exit via a small 3/8 hole.
The above saw that has the replacement carb and the muffler opened up will run like and older 026 and it will last longer.The saw will now run cooler then it did from the factory.
The extra power gains that the saw has now verses engine design,really isn't an issue.
Later
Dan

 

[glens]

I wonder about a little can of worms here.  If the newer saw is built to accommodate the greater heat, what happens when we make the saw to run cooler?  Is there a chance we can get it too cool?

I intently compared my 036 with my neighbor's 034S and the main differences other than the carburetor adjustment range and muffler are that the newer cylinder has more and thinner fins as well as a metal shroud behind the muffler to duct cooling air. (I wish I'd paid certain attention to the fan configuration, but did not, so that factor is up in the air, but it wouldn't surprise me if the fan were higher capacity on the newer saw).

Would it be possible that the engine could run too cool if I were to open the exhaust tract and did nothing else?

Also, according to what I've heard, the fixed-jet carbs on the Stihl 260 (maybe stuff in general?) should no longer be present in the distribution pipeline.

I've brought this subject up before within other threads.  I'm confident that whereas the typical bottom end might hold up to a few stock top end rebuilds, it would certainly fail sooner with a modded top end.

This whole bit about Stihl v. Husky and how the latter responds better to mods reminds me of the Japanese motorcycle industry back in the early 80's.  If you wanted a good complete bike ready to go out of the shop you bought the Honda, but if you wanted one to hop up, you'd get the Kawasaki.  I don't know what the current situation in that arena is, but it's obvious the manufacturing mindset is still popular.

Glen

 

[Marky Mark]

Here's a shot of the one Dan Henry made for my 260. For some reason I like the sidepipes.

 

[mryb]

Im sending all my side pipes away to get chromed...Rick/Creep

 

[Jacob J.]

123Michael- It depends on the model of Stihl you have. The MS-260 has a top RPM of 13,500 stock. Your saw may be an older model designed to top out at 10,000 rpm. Different saws are designed for different load and RPM ranges, just like vehicles. I'm only hoping they come out with a propane powered saw soon so if I run out of fuel I can hook up to my campstove.

Glens asks an interesting question- Recently, several log cutters here bought 360s and opened up the mufflers. The saws would never run right. So they switched back to the stock mufflers and they ran perfectly.

 

[dozerdan]

glens
I am not sure what thread that you replied to but I don't think that is was the correct one.This one is about the 260,not the 034S,036 or the Husky vs. Stihl.
I will answer your questions that are worthwhile.
"If the newer saw is built to accommodate the greater heat"
The key word here is if.I have seen more 026s and the 260 with melted pistons then any other saw.I would say that the saw is not designed for the cylinder temperatures that they create.
"Also, according to what I've heard, the fixed-jet carbs on the Stihl 260 (maybe stuff in general?) should no longer be present in the distribution pipeline."
I don't think that we will ever see the 260 with a fully adjustable carb,without the fixed main jet.I am sure they will drop the 260 to sell more of their 270 and 280 models.
JJ
Did you change carbs on those new 360s after the mufflers work was done?Did they run lean?
Later
Dan

 

[glens]

Dan,

I guess you were trying to make some sort of point, but it was lost on me.  This thread, at the point I "arrived", was talking about less heat in a modified engine.  I took that thought and went with it a little, as well touching on another point brought up in the course of the thread.  The two saws I used in my example are virtually identical yet one is clearly designed to operate with EPA-resultant conditions and in fact the two saws do perform quite similarly.

Thanks for your opinions on the couple of items you touched.  I'd guess if the piston melted it was operating out of design heat range, beyond the capability of flywheel fans and shrouded cylinder fins.  How about the other (main?) question?  Can one over-cool an engine?  What might some of the consequences of doing so be?

Glen

 

[123Michael]

Yes, i didnt consider your EPA restrictions. I am from australia and often see car manuals that cover US engines as well. The US engines seem to often have an extra cat converter and an extra oxygen sensor (and a few other bits and peices) to meet the californian EPA laws. So i guess your EPA laws are more restrictive than ours. If that is the case then your saws are more than likely over engineered to tolerate the higher revs.

A second point about running an engine too cold is a good one. From my experience in the auto industry i found a lot of customers would remove their thermostat thinking they were doing their engine a favour. however, most damage is done to an auto engine when it is cold. the engine is designed to operate with the least amount of friction when at its optimum operating temperature. Question whether a stihl is designed the same way.

 

[jokers]

If Stihls had Turbos and Air Injection their pistons would never melt!

Russ

 

[SilverBlue]

^ PHHHHHH

 

[rahtreelimbs]

Originally posted by jokers
If Stihls had Turbos and Air Injection their pistons would never melt!

Russ

Not needed if people would do proper maintainance. In other words clean the air filter when needed!

 

[Gypo Logger]

Ok, picture this in your mind and then tell me what you think about 2 cycle saw mods.
Here we have Larry the Logger who is very hard on his stock 044, never cleans it, forces it thru the cut and generally fooks the saw long before its useful life is over.
Then we have Woodtick Willy, who always cleans and looks after his JD 044.
Who's saw do you think will last longer?
It generally goes with the territory that one will look after their saw more, just by virtue of the fact that they made the investment to get their saw hopped up a bit.
However the most eloquent words ever spoken on AS were by Professor Walt Galer, " The faster the saw, the better the dirt works". Just ask the Truffle Hound if you dont believe me.
John

 

[123Michael]

Larry the logger should be ashamed, how does he sleep at night.

Lets say we compare apples with apples, and clean saws with clean saws.

 

[Gypo Logger]

Hi Michael, the problem is that the powerhead, stock or modified, doesnt do the cutting. It is by far the chain.
So to answer your question with regards to longevity, we would have to talk in terms of how much wood was cut, stock v.s. reworked, plus the umpteen other factors that enter into it.
All I can offer is try it yourself then you tell me.
John

 

[Jacob J.]

Most woodticks don't replace the air filter after 25 hours of operation as recommended by the factory I'll bet. I've found even with careful maintenance a stock filter for any model of Stihl is only good for about 100 hours. Most Huskies are far less due to air injection.